Rapidly indicating bridge



June 5, 1956 Filed Jan. 18, 1952 c. M. RlvELY 21,749,510

RAPIDLY INDICATING BRIDGE 2 Sheets-Sheet l E F022 EXAMPLE 4 P//ara Raum/IMP ELL if INVENTOR aM. en/Ez Y.

BY n g.;

ATTORNEY 2 Sheets-'Sheet 2 Filed Jan. 18, 1952 aan HMP 6067.5 HM P A p m M m I||1|11|||I|.w|, mx |||v l||| il IP w WZ w f M :www m n N l I|l|||||l m E -|1 ||l-ll- C W Wg a! r C NL la. Za M l m@ M l@ A F m kbl 5 1|.|x|. .In f i z A ||1|||1 ,I m4 3, N el- Wills! ,W MQ l r #Y re E E m Y a a a r a@ r Wm Wm w W4 E z y e L ma 5./ E 6 P r 0 y W m WW T m V W E f n i@ w M l 0 a y E Fw r a, Ta w INVENTOR C. M. E/VEL Y.

Y ATTORNEY United States Patent O RAPIDLY INDICATING BRIDGE Clair M. Rively, Rockaway, N. J., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application January 18, 1952, Serial No. 267,152

7 Claims. (Cl. 324-62) My invention relates to testing apparatus and, more particularly to an apparatus for testing photoflash lamps.

it is dicult to test the filament of photoflash lamps due to the fact that even a small current through the lament is likely to ilash the lamp. Consequently, the apparatus used to test photoash lamps can only send a very small current through the lament which means that the apparatus must be extremely sensitive. However, the usual testing apparatus, which consists of a bridge and a slow moving galvanometer type indicator, or of elaborate electronic apparatus to make the more rapid indicating type instruments insensitive to line voltage variations, are unsatisfactory for use in production.

Therefore, the principal object of the invention is to provide an accurate testing means which is rapidly indicating and which can be used in the production of photoash lamps.

Another object of the invention is to provide a testing means which depends upon a phase shift to indicate the change in resistance of an electrical element.

The further object of the invention is to provide a means of testing the filaments of photoash lamps, which means shall be accurate and substantially independent of the Voltage supplied to the testing means.

The above objects, and the other objects which will become apparent as the description proceeds, are effected by measuring the unknown resistance with a bridge network, using the output signal from the bridge network to control the relative phase shift of a pulsing apparatus, and using the output pulse of the pulsing apparatus to control the tiring of a thyratron which controls the current ilowing through a signal indicator.

The novel features that I consider characteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, may be best understood from the following description or specific embodiments when read in conjunction with the accompanying drawings in which:

Figure 1 is a schematic drawing of the circuit used in our testing apparatus.

Figure 2 shows the wave forms at various points of the `testing circuit.

To indicate whether a filament is acceptable the resistance of the iilament of a photoliash 12 is tested by connecting the lamp into `Wheatstone bridge 14. We prefer to use a Wheatstone bridge although any suitable bridge means can be used. The bridge 14 has power input terminals 16 and 18 and signal output terminals 2u and 22. The filament 19 is connected between terminals 16 and 22 and forms one leg of the Wheatstone bridge. The other legs of the bridge are formed by connecting resistor 24 between terminals i8 and 22, resistor 26 between terminals 1S and 20, and resistor 28 between terminals Zit and 16. The power supply for the bridge is preferably a 6.3 volts A. C. supply furnished by transformer 29 which has its primary connected to a ll() v. A. C. supply. The secondary of transformer 29 is connected to terminals i6 and 18 through current limiting 2 resistors 30 and 32. Also connected between the input terminals 16 and 18 is a potentiometer 34 whose sliding arm connection is connected to the output terminal 20. This potentiometer provides a means for adjusting bridge 14.

The output signal from the bridge is coupled to an activable controllable pulsing network 36 through a coupling transformer 38. The pulsing network is comprised of two vacuum tubes 39 and 40 which are at least 3 element tubes, including a control element, connected as a multi-vibrator. In the multi-vibrator network the cathodes of the tubes 39 and 40 are connected to the B- terminal of the D. C. power supply which is at ground potential by the common resistor 41. The plates of the tubes 39 and 40 are connected to the B+ terminal of the D. C. power supply through resistors 42 and 43 respectively in the plate circuits. The plate of tube 39 is also connected to the grid 44 of tube 4u by a condenser 46, the grid 44 in turn being connected to ground by the grid biasing resistor 47. The charging and discharging of the condenser 46 governs the conduction of tube 40 so that the tube 40 will conduct only when tube 39 is not conducting. As the current shifts from one tube to the other, a voltage pulse will occur across resistor 4i in the cathode circuit of tubes 39 and 40 as shown by curve 4S in Figure 2.

The conduction of tubes 39 and 40 and consequently the pulsed voltage across resistor 41 is controlled by an A. C. synchronizing signal voltage impressed between the grid Sti and the cathode of tube 39. The A. C. signal voltage is derived from the voltage drop across part of a potentiometer 52 and the voltage drop across the secondary of coupling transformer 38. The grid 50 is connected to the center tap of potentiometer 52 through the secondary of coupling transformer 33. One end of the potentiometer 52 is connected to ground. The other end of the potentiometer is connected to junction 54 on one side of the A. C. ll() volt supply by condenser 56. The junction 57 on the other side of the il() volt A. C. supply is connected to ground through a resistor 58 thus completing an A. C. circuit through potentiometer 52. The controlling A. C. synchronizing signal voltage between the grid Si) and the cathode of tube 39 is the sum of the voltage drop E1 across the secondary of the coupling transformer 38 and the voltage drop E2; between the center tap of the potentiometer 52 and ground. The output pulses across resistor 41 will synchronize with the voltage (E1 E7.) just as the voltage starts negative. This can be seen by comparing the multi-vibrator output curve 48 and the (El J,- E2) curve in Figure 2.

The output pulses of the multi-vibrator network 36 appearing across the resistor 41 control the current through the thyratron tube 62. The plate and cathode of the thyratron are connected in series with an indicator lamp 63 between junctions 54 and 57 on the A. C. supply. The output pulses from the multi-vibrator across resistor 41 are applied to grid 64 of the thyratron by connecting the grid to the cathodes of tubes 39 and 4d by condenser 66 and to ground by resistor 63. The resistor 68 and condenser 66 constitute a differentiating network, and their values are chosen so as to produce sharp pointed pulses on the grid 64 of the thyratron 62 as shown by curve 69 of Fig. 2.

The cathode of the thyratron 62 is also connected to ground by resistor 58. A circuit for furnishing D. C. bias on the thyratron is completed by connecting the thyratron cathode to the B-I- terminal of the D. C. power supply by resistor 70. Resistor 58 between the thyratron cathode and ground and resistor 70 constitute a voltage dividing network applying bias to the thyratron. If desired, a condenser 72 may be connected between the plate of the 3 tube 46 and ground to increase the magnitude of the pulses appearing on the grid 64 of the thyratron 62.

The relative phase of the pulses on the grid of the thyratron 62 with respect to the periodic varying reference voltage on the plate of the thyratron 62 determines the current through thyratron 62 and indicating lamp 63. The thyratron is biased so it will conduct when the pulse is in phase with the alternating Voltage across the plate of the cathode thyratron 62, i. e. when the voltage pulse on the grid 64 occurs at the peak of the positive wave across the plate and cathode of the thyrathon 62. The pulses have the same periodicity as the reference voltage on the plate of the thyratron 62. The phase of the pulse With respect to the reference voltage is controlled by the relative phase of the activating and controlling alternating voltage on the grid of Vacuum tube 39. The pulse will occur when the activating voltage starts negative. The periodicity of the activating voltage is the same as that of the reference voltage.

The controlling voltage on the grid of vacuum tube 39 is the sum of voltages E1 and E2 where E1 is the secondary voltage of transformer 38, and E2 is the divided voltage across potentiometer S2. Condenser 56 and potentiometer 52 are so chosen in value that the voltage E2 is 90 leading the A. C. supply voltage. The voltage E1 is in phase or 180 out of phase with the supply voltage depending on the imbalance of bridge 14; and, therefore, El is 90 leading or lagging E2. For a good lament the bridge has no output and the Voltage E14-E2 is the same as voltage E2 which activates and synchroL nizes the pulsing circuit output voltage in phase with the thyratron plate voltage. If the resistance of the filament is too high, the bridge has an output signal voltage E2 and the voltage E1+E2 changes the relative phase of the output pulses of the pulsing circuit 36 with respect to the thyratron line voltage so that the thyratron 62 does not tire. Similarly, if the filament resistance is too low the output of the bridge 14 shifts the phase of the output of the pulsing circuit 36 in the opposite direction also extinguishing the lamp. Therefore it can be seen that the thyratron and associated circuit functions as a phase discriminator. The limits of lamp resistance which will extinguish the indicator lamp 50 may be adjusted by varying E2 across potentiometer 52.

While my testing apparatus has been designed specifically for testing photoflash lamp filaments, it can be used to test and measure electrical characteristics Wherever it is necessary to indicate whether or not the electrical characteristics of an unknown is within definite limits. it will be also obvious to one skilled in the art that by replacing the thyratron 62 and lamp 63 with a phase detector which will indicate the exact phase shift, rather than limits of the phase shift, of the output of the multi-vibrator with respect to the A. C. line voltage, direct values of resistance can be determined. inasmuch as indication from the circuit depends upon a shift of phase, the testing circuit is independent of fluctuations in the 110 volt A. C. supply and can be used to measure resistances through which only a small current can be passed. The bridge is also rapid indicating and is suit able for use in the mass production of photoash lamps.

While i have shown and described a specific embodiment of my invention, I am fully aware that many modifications thereof are possible. I do not intend to be restricted therefore, except as is necessitated by the scope and the spirit of the appended claims.

i claim:

l. A testing circuit to determine when the resistance of an element is Within predetermined limits comprising a Wheatstone bridge having said element connected into one leg thereof, the magnitude and phase of the output of said Wheatstone bridge depending upon the resistance of said element, phase indicating means comprising a thyratron having pulses applied to its grid and a reference voltage applied to its plate, said indicating means being capable of determining when the phase of said pulse with respect to said reference Voltage is shifted a predetermined amount, a controllable pulsing network to provide said pulses, the output pulses of said network being synchronized with a point on an input voltage wave to said pulsing network, means supplying an input voltage wave to said pulsing network which causes said pulses to occur at the peak of the positive wave of said reference voltage, means to shift the phase of said reference voltage, said bridge being connected to said pulsing network through a voltage adding means to add the output of said bridge to said phase shifted reference voltage so that the output signal from said bridge varies the magnitude and phase of said input wave thereby causing the phase of the output pulses with respect to said reference voltage to shift in an amount dependent upon the phase and magnitude of the output signal from said bridge, the phase of said pulses being shifted in one direction when the resistance of said element is high and in the other direction when the resistance of said element is low.

2. A testing apparatus comprising a resistance comparing means having an input connected to a reference alternating current voltage and an output voltage which is either zero, in phase with said reference voltage or degrees phase shifted with respect to said reference voltage dependent upon the magnitude of the resistance being compared, phase shifting means having an input connected across said reference voltage and an output voltage Whose phase is shifted with respect to said reference voltage, voltage adding means to add said phase shifting means output voltage with said comparing means output voltage, and a phase shift indicating means having applied thereto said added voltage and said reference voltage for indicating when said added voltage differs in phase from said reference voltage by a predetermined amount.

3. A testing apparatus comprising a resistance comparing means having an input connected to a reference alternating current voltage and an output voltage which is either zero, in phase with said reference voltage or 180 degrees phase shifted with respect to said reference voltage dependent upon the magnitude of the resistance being compared, phase shifting means having an input connected across said reference voltage and an output voltage whose phase is shifted with respect to said reference voltage, adjustable controlling means to control the amplitude of said phase shifting means output voltage, voltage adding means to add said phase shifting means output voltage with said comparing means output voltage, and a phase shift indicating means having applied thereto said added voltage and said reference voltage for indicating when said added voltage differs in phase from said reference voltage by a predetermined amount.

4. A testing apparatus comprising a resistance comparing means having an input connected to a reference alternating current voltage and an output voltage which is either zero, in phase with said reference voltage or 180 degrees phase shifted with respect to said reference voltage dependent upon the magnitude of the resistance being compared, phase shifting means having an input connected across said reference voltage and an output voltage whose phase is shifted with respect to said reference voltage, adjustable controlling means to control the amplitude of said phase shifting means output voltage, voltage adding means to add said phase shifting means output voltage with said comparing means output voltage, pulsing means to convert said added voltage into pulses, and a phase shift indicating means having applied thereto said pulses and said reference voltage for indicating when said pulses differ in phase from said reference voltage by a predetermined amount.

5. A testing apparatus to determine when the resistance of an element is within predetermined limits comprising, a Wheatstone bridge having said element connected into one leg thereof, said bridge having an input connected to a reference alternating current voltage and an output voltage which is either zero, in phase with said reference` voltage or 180 degrees phase shifted with respect to said reference voltage dependent upon the magnitude of the resistance being compared, phase shifting means having an input connected across said reference voltage and an output voltage whose phase is shifted with respect to said reference voltage, voltage adding means to add said phase shifting means output voltage with said Wheatstone bridge output voltage, and a phase shift indicating means having applied thereto said added voltage and said reference voltage for indicating when said added voltage differs in phase from said reference voltage by a predetermined amount.

6. A testing apparatus to determine when the resistance of an element is within predetermined limits comprising, a Wheatstone bridge having said element connected into one leg thereof, said bridgehaving an input connected to a reference alternating current voltage and an output voltage which is either zero, in phase with said reference voltage or 180 degrees phase shifted with respect to said reference voltage dependent upon the magnitude of the resistance being compared, phase shifting means having an input connected across said reference voltage and an output voltage Whose phase is shifted with respect to said reference voltage, adjustable controlling means to control the amplitude of said phase shifting means output voltage, voltage adding means to add said phase shifting means output voltage with said Wheatstone bridge output voltage, pulsing means to convert said added voltage into pulses, and a phase shift indicating means having applied thereto said pulses and said reference voltage for indicating when said pulses differ in phase from said reference voltage by a predetermined amount.

7. A testing apparatus comprising a Wheatstone bridge adapted for receiving an unknown resistance in one leg thereof and having input and output terminals, an input transformer having said bridge input terminals connected across the secondary thereof and a reference A. C. potential connected across the primary thereof, said bridge being grounded at a point intermediate its output terminals, a bridge output voltage being developed across said bridge output terminals, said bridge output voltage being either zero, in phase with said reference Voltage or 180 degrees phase shifted with respect to said reference voltage dependent upon the magnitude of said unknown resistance, a reference voltage phase shifting means having input and output terminals, said phase shifting means input terminals being connected across said transformer primary and said phase shifting means output terminals having a voltage developed thereacross which is phase shifted with respect to said reference voltage, adjustable controlling means to control the amplitude of said phase shifting means output voltage, voltage adding means having applied thereto said bridge output voltage and said phase shifting means output voltage, said voltage adding means being adapted to add said bridge output voltage and said phase shift reference voltage, pulsing means to convert said added voltage into pulses, indicating means comprising a thyratron having said pulses applied to its grid and said reference voltage applied to its plate, said thyratron being so biased that when the phase of said pulse with respect to said reference voltage is shifted a predetermined amount the thyratron will fire.

References Cited in the file of this patent UNITED STATES PATENTS 2,335,265 Dodington Nov. 30, 1943 2,455,646 Beard Dec. 7, 1948 2,470,412 Piety May 17, 1949 2,474,692 Rossoff June 28, 1949 2,505,072 Sunstein Apr. 25, 1950 

